Phosphorescent four-coordinated platinum (II) complex

ABSTRACT

A phosphorescent four-coordinated platinum (II) complex represented by formula (C) is disclosed: 
     
       
         
         
             
             
         
       
         
         
           
             where Y represents N or P; R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 9 , R 10 , R 11 , and R 12  are the same or different, and independently represent hydrogen, or a substituted or unsubstituted organic group; and 
           
         
       
    
                         
represents
 
                         
or

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Patent Application No.102119777, filed on Jun. 4, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a phosphorescent four-coordinated platinum (II)complex, more particularly to a phosphorescent four-coordinated platinum(II) complex containing two specific monoanionic bidentate ligandschelating with a platinum (II) central metal atom.

2. Description of the Related Art

An organic light emitting diode (hereinafter referred as OLED) needs amaterial that could be excited to emit a visible light so as to serve asan emitting layer. Conventionally, a compound having an emission peakmaximum ranging from 470 nm to 530 nm has inferior blue light emissionefficiency.

In general, a phosphorescent four-coordinated platinum (II) complex isused as a blue light emission material for OLED. For example, U.S. Pat.No. 6,963,005 discloses a four-coordinated platinum (II) complex formedby chelating a monoanionic O,O-bidentate ligand and a monoanionicC,P-bidentate ligand with a platinum (II) central atom.

Inorg. Chem., 2007, 11202-11212 discloses a four-coordinated platinum(II) complex that has a maximum quantum yield of 56% in solid state andthat is represented by the following formula:

where

Y represents substituted or unsubstituted pyrazolate or chloridesubstituents.

The thesis of Yao-Te Yen of National Tsing Hua University, 2008,GH000943467 discloses a four-coordinated platinum (II) complex that hasa quantum yield of 0% both at room temperature and in dichloromethanesolution. The four-coordinated platinum (II) complex is represented bythe following formula:

where

X represents hydrogen or fluorine;

Ar represents a fluorine-substituted or unsubstituted phenyl group;

R represents Ar or a methyl group; and

L represents chloride or an isothiocyanato group.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide aphosphorescent four-coordinated platinum (II) complex that could beexcited to emit blue light or blue-green light and that has superiorblue light emission quantum yield.

According to the present invention, there is provided a phosphorescentfour-coordinated platinum (II) complex represented by formula (C):

where

Y represents N or P;

R¹, R², R³, R⁴, R⁵, R⁶, R⁹, R¹⁰, R¹¹, and R¹² are the same or different,and independently represent hydrogen, or a substituted or unsubstitutedorganic group; and

represents

or

when

represents

X represents C—R⁸ or nitrogen; R⁷ represents a substituted orunsubstituted organic group; and R⁸ represents hydrogen or a substitutedor unsubstituted organic group; and

when

represents

ring A represents a substituted or unsubstituted bridged carbocyclicring.

Preferably, the phosphorescent four-coordinated platinum (II) complexaccording this invention includes a platinum (II) central atom, amonoanionic N,N-bidentate ligand (i.e., the monoanionic bidentate ligand

in formula (C) where Y is N) chelating with the platinum (II) centralatom, and a monoanionic C,P-bidentate ligand (i.e., the monoanionicbidentate ligand

in formula (C)) chelating with the platinum (II) central atom.

When the phosphorescent four-coordinated platinum (II) complex accordingto this invention is excited, the complex could emit blue light orblue-green light and has superior blue light emission quantum yield.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiment with reference to the accompanying drawing:

FIG. 1 is a visible spectrum that illustrates emission wavelength rangesof complexes E1 to E7 and CE obtained from Examples 1 to 7 andComparative Example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A phosphorescent four-coordinated platinum (II) complex according to thepresent invention is represented by formula (C):

where

Y represents N or P;

R¹, R², R³, R⁴, R⁵, R⁶, R⁹, R¹⁰, R¹¹, and R¹² are the same or different,and independently represent hydrogen, or a substituted or unsubstitutedorganic group; and

represents

or

when

represents

X represents C—R⁸ or nitrogen; R⁷ represents a substituted orunsubstituted organic group; and R⁸ represents hydrogen or a substitutedor unsubstituted organic group; and

when

represents

ring A represents a substituted or unsubstituted bridged carbocyclicring.

The inventors found that in the phosphorescent four-coordinated platinum(II) complex of the present invention, both the monoanionic bidentateligand

(where Y is N or P, and is preferably N) as a chromophore and themonoanionic bidentate ligand

chelate with the platinum (II) central atom so as to regulate an energygap between the highest occupied molecular orbital (referred as HOMO)and the lowest unoccupied molecular orbital (referred as LUMO) of thephosphorescent four-coordinated platinum (II) complex. Accordingly, thephosphorescent four-coordinated platinum (II) complex of the presentinvention could emit phosphorescence with an emission peak maximumranging from 470 nm to 530 nm (i.e., blue light to blue-green light)when the complex is excited.

In addition, the inventors believe that in the phosphorescentfour-coordinated platinum (II) complex according to this invention, thebenzylphosphino moiety of the monoanionic bidentate ligand

can reduce the molecular stacking between the phosphorescentfour-coordinated platinum (II) complexes and can avoid a tripletmetal-metal-to-ligand charge transfer transition (referred as ³MMLCT)occurred in the common blue-emitting platinum (II) metal complexes.Therefore, the phosphorescent four-coordinated platinum (II) complexaccording to this invention emits the phosphorescence with significanthypsochromic shift (blue shift) and has good solubility to commonorganic solvents.

Preferably, Y represents N; R¹ and R² independently represent asubstituted or unsubstituted phenyl group; R³, R⁴, R⁵, and R⁶independently represent hydrogen, a C₁-C₁₃ alkyl group, or a substitutedor unsubstituted aryl group with the proviso that at least one of R³,R⁴, R⁵, and R⁶ is not hydrogen; R⁹, R¹⁰, R¹¹, and R¹² independentlyrepresent hydrogen, a C₁-C₄ alkyl group, or a C₁-C₄ haloalkyl group; R⁷represents a C₄-C₁₂ alkyl group, a C₁-C₄ haloalkyl group, or asubstituted or unsubstituted aryl group; R⁸ represents hydrogen, aC₁-C₁₂ alkyl group, a C₁-C₄ haloalkyl group, or a substituted orunsubstituted aryl group; and the ring A represents a substituted orunsubstituted C₆-C₁₀ bridged carbocyclic ring.

Preferably, R⁵ represents a tert-butyl group or a 2,6-diisopropyl phenylgroup.

Preferably, R⁷ represents a tert-butyl group, a trifluoromethyl group,or a 2-trifluoromethyl phenyl group.

Preferably, R¹⁰ represents hydrogen or a trifluoromethyl group.

Preferably, R³, R⁴, and R⁶ represent hydrogen.

Preferably, the phosphorescent four-coordinated platinum (II) complexaccording to this invention has an emission peak maximum ranging from470 nm to 530 nm, and more preferably from 470 nm to 500 nm.

The present invention will now be further described by way of thefollowing examples. It is understood that the following examples areused for illustration, and should not be construed as limiting theimplementation of the present invention.

Synthesis of Precursor Solution (PS) of Phosphorescent Four-CoordinatedPlatinum (II) Complex Synthesis Example 1 PS1

Pt(tht)₂Cl₂ (synthesized according to a method disclosed in J. Chem.Soc., Dalton Trans. 1980, 888-894; 100 mg, 1 eq, “tht” representstetrahydrothiophene), benzyldiphenylphosphine purchased from Alfa Aesar(68 mg, 1.1 eq), and sodium acetate (94 mg, 5 eq) were added in a 50 mLround-bottomed flask, and degassed xylene (purchased from ECHOChemical;Product no: XA2101-000000-72EC; 6 mL) was then added therein with mixingto obtain a mixture, followed by heating to 100° C. and reacting for 12hours. The mixture was then cooled to room temperature, and a precursorsolution (PS1) of a phosphorescent four-coordinated platinum (II)complex was obtained.

Synthesis Example 2 PS2

Pt(tht)₂Cl₂ (100 mg, 1 eq), diphenyl(4-trifluoromethylbenzyl)phosphine(86 mg, 1.1 eq) synthesized according to a method disclosed in JP2008-010647, and sodium acetate (94 mg, 5 eq) were added in a 50 mLround-bottomed flask, and degassed xylene (6 ml) was then added thereinwith mixing to obtain a mixture, followed by heating to 100° C. andreacting for 12 hours. The mixture was then cooled to room temperature,and a precursor solution (PS2) of a phosphorescent four-coordinatedplatinum (II) complex was obtained.

Synthesis of Phosphorescent Four-Coordinated Platinum (II) ComplexExample 1 E1

3-(4-(tert-butyl)pyridin-2-yl)-7,8,8-trimethyl-4,5,6,7-tetrahydro-2H-4,7-methanoindazole(70 mg, 1 eq) was added into the PS1 obtained from Synthesis Example 1to obtain a mixture, and the mixture was heated to 100° C. and reactedfor 6 hours, followed by cooling to room temperature and removing thesolvent. Silica-gel column chromatography was conducted to purify themixture using an eluent of ethyl acetate (hereinafter referred as EA)and n-hexane (EA:n-hexane=1:3 (by volume)). Recrystallization was thenconducted using dichloromethane/n-hexane so as to obtain a whitecrystalline product, referred to as complex E1 (77.4% yield; 137 mg).The reaction scheme for producing the complex E1 is represented asfollows:

The spectrum analysis for the complex E1 is: ¹H NMR (400 MHz, CD₂Cl₂,298 K) δ 8.97 (d, J=8.1 Hz, 1H), 7.84 (dd, J=10.4, 18.3 Hz, 4H),7.38-7.51 (m, 8H), 7.06-7.07 (m, 2H), 6.94 (t, J=7.2 Hz, 1H), 6.47 (dd,J=1.8, 6 Hz, 1H), 3.73 (d, J=11.2 Hz, 2H), 2.97 (d, J=3.7 Hz, 1H),2.08-2.14 (m, 1H), 1.80-1.86 (m, 1H), 1.43-1.47 (m, 1H), 1.41 (s, 3H),1.25 (s, 9H), 0.97 (s, 3H), 0.84-0.88 (m, 1H), 0.81 (s, 3H) ppm, ³¹P NMR(200 MHz, CDCl₃, 298 K) δ 36.38 ppm, FAB-MS m/z 779.7 [M+1]⁺.

Example 2 E2

4-(tert-butyl)-2-(3-(tert-butyl)-1H-pyrazol-5-yl)pyridine (59 mg, 1 eq)was added into the PS1 obtained from Synthesis Example 1 to obtain amixture, and the mixture was heated to 100° C. and reacted for 6 hours,followed by cooling to room temperature and removing the solvent.Silica-gel column chromatography was conducted to purify the mixtureusing an eluent of dichloromethane and n-hexane(dichloromethane:hexane=1:1 (by volume)). Recrystallization was thenconducted using dichloromethane/n-hexane so as to obtain a light yellowcrystalline product, referred to as complex E2 (59.9% yield; 98.9 mg).The reaction scheme for producing the complex E2 is represented asfollows:

The spectrum analysis for the complex E2 is: ¹H NMR (400 MHz, CD₂Cl₂,298 K) δ 9.05 (d, J=7.6 Hz, 1H), 7.86-7.91 (m, 3H), 7.62 (d, J=2.0 Hz,1H), 7.46-7.54 (m, 5H), 7.26-7.31 (m, 2H), 7.17 (d, J=7.0 Hz, 1H),6.98-7.11 (m, 4H), 6.60 (s, 1H), 3.80 (d, J=11.4 Hz, 2H), 1.44 (s, 9H),1.28 (s, 9H) ppm, ³¹P NMR (200 MHz, CD₂Cl₂, 298 K) δ 36.68 ppm, FAB-MSm/z 727.7 [M+1]⁺.

Example 3 E3

4-(tert-butyl)-2-(3-(tert-butyl)-1H-1,2,4-triaz ol-5-yl)pyridine (59 mg,1 eq) was added into the PS1 obtained from Synthesis Example 1 to obtaina mixture, and the mixture was heated to 100° C. and reacted for 6hours, followed by cooling to room temperature and removing the solvent.Silica-gel column chromatography was conducted to purify the mixtureusing an eluent of EA and n-hexane (EA:n-hexane=1:2 (by volume)).Recrystallization was then conducted using dichloromethane/n-hexane soas to obtain a light yellow crystalline product, referred to as complexE3 (44% yield; 73 mg). The reaction scheme for producing the complex E3is represented as follows:

The spectrum analysis for the complex E3 is: ¹H NMR (400 MHz, CD₂Cl₂,298 K) δ 8.97 (d, J=7.2 Hz, 1H), 8.05 (s, 1H), 7.84-7.89 (m, 4H),7.52-7.56 (m, 3H), 7.46-7.50 (m, 4H), 7.17 (d, J=6.8 Hz, 1H), 6.97-6.79(m, 2H), 6.78 (dd, J=2.2, 6 Hz, 1H), 3.80 (d, J=11.4 Hz, 2H), 1.48 (s,9H), 1.31 (s, 9H), ³¹P NMR (200 MHz, CD₂Cl₂, 298 K) δ 36.32, FAB-MS m/z728.1 [M+1]⁺.

Example 4 E4

4-(tert-butyl)-2-[3-(2-trifluoromethylphenyl)-1H-1,2,4-triazol-5-yl]pyridine (80 mg, 1 eq) was added into the PS1obtained from Synthesis Example 1 to obtain a mixture, and the mixturewas heated to 100° C. and reacted for 6 hours, followed by cooling toroom temperature and removing the solvent. Silica-gel columnchromatography was conducted to purify the mixture using an eluent ofdichloromethane and n-hexane (dichloromethane:n-hexane=1:3 (by volume)).Recrystallization was then conducted using dichloromethane/n-hexane soas to obtain a white crystalline product, referred to as complex E4(77.2% yield; 144 mg). The reaction scheme for producing the complex E4is represented as follows:

The spectrum analysis for the complex E4 is: ¹H NMR (400 MHz, CDCl₃, 298K) δ 9.07 (d, J=7.9 Hz, 1H), 8.17 (d, J=2.0 Hz, 1H), 7.99 (d, J=7.7 Hz,1H), 7.83-7.88 (m, 4H), 7.79 (d, J=7.7 Hz, 1H), 7.56-7.62 (m, 2H),7.44-7.53 (m, 7H), 7.08-7.15 (m, 2H), 6.99 (t, J=7.1 Hz, 1H), 6.79 (dd,J=2.2, 6 Hz, 1H), 3.80 (d, J=11.4 Hz, 2H), 1.29 (s, 9H), ¹⁹F NMR (400MHz, CDCl₃, 298 K) δ −58.2, ³¹P NMR (200 MHz, CDCl₃, 298 K) δ 36.35,FAB-MS m/z 815.8 M⁺.

Example 5 E5

4-(tert-butyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (61 mg, 1eq) was added into the PS1 obtained from Synthesis Example 1 to obtain amixture, and the mixture was heated to 100° C. and reacted for 6 hours,followed by cooling to room temperature and removing the solvent.Silica-gel column chromatography was conducted to purify the mixtureusing an eluent of dichloromethane and n-hexane(dichloromethane:n-hexane=1:1 (by volume)). Recrystallization was thenconducted using dichloromethane/n-hexane so as to obtain a light yellowcrystalline product, referred to as complex E5 (60.8% yield; 102 mg).The reaction scheme for producing the complex E5 is represented asfollows:

The spectrum analysis for the complex E5 is: ¹H NMR (400 MHz, CDCl₃, 298K) δ 8.89 (d, J=8.3 Hz, 1H), 7.83 (dd, J=8.1, 11.7 Hz, 4H), 7.61 (d,J=1.4 Hz, 1H), 7.56 (d, J=6.1 Hz, 1H), 7.42-7.51 (m, 6H), 7.11 (t, J=6.4Hz, 2H), 6.98 (t, J=7.4 Hz, 1H), 6.94 (s, 1H), 6.64 (dd, J=2.1, 6.1 Hz,1H), 3.77 (d, J=11.4 Hz, 2H), 1.26 (s, 9H), ¹⁹F NMR (400 MHz, CDCl₃, 298K) δ −60.7, ³¹P NMR (200 MHz, CDCl₃, 298 K) δ 36.24, FAB-MS m/z 738.7M⁺.

Example 6 E6

4-(2,6-diisopropylphenyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine(84 mg, 1 eq) was added into the PS1 obtained from Synthesis Example 1to obtain a mixture, and the mixture was heated to 100° C. and reactedfor 6 hours, followed by cooling to room temperature and removing thesolvent. Silica-gel column chromatography was conducted to purify themixture using an eluent of dichloromethane and n-hexane(dichloromethane:n-hexane 1:1). Recrystallization was then conductedusing dichloromethane/n-hexane so as to obtain a light yellowcrystalline product, referred to as complex E6 (44.3% yield; 85 mg). Thereaction scheme for producing the complex E6 is represented as follows:

The spectrum analysis for the complex E6 is: ¹H NMR (400 MHz, CDCl₃, 298K) δ 8.85 (d, J=8.3 Hz, 1H), 7.85-7.90 (m, 4H), 7.63 (d, J=5.7 Hz, 1H),7.42-7.51 (m, 7H), 7.35 (t, J=7.8 Hz, 1H), 7.18 (d, J=7.8 Hz, 2H),7.13-7.16 (m, 2H), 7.00 (t, J=7.4 Hz, 1H), 6.88 (s, 1H), 6.47 (dd,J=1.7, 5.7 Hz, 1H), 3.82 (d, J=11.4 Hz, 2H), 2.41 (hept, J=6.8 Hz, 2H),1.10 (d, J=6.8 Hz, 6H), 0.99 (d, J=6.8 Hz, 6H), ¹⁹F NMR (400 MHz, CDCl₃,298 K) δ −60.7, ³¹P NMR (200 MHz, CDCl₃, 298 K) δ 36.81, FAB-MS m/z842.9 M⁺.

Example 7 E7

4-(tert-butyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (61 mg, 1eq) was added into the PS2 obtained from Synthesis Example 2 to obtain amixture, and the mixture was heated to 100° C. and reacted for 6 hours,followed by cooling to room temperature and removing the solvent.Silica-gel column chromatography was conducted to purify the mixtureusing an eluent of dichloromethane and n-hexane(dichloromethane:n-hexane=1:1). Recrystallization was then conductedusing dichloromethane/n-hexane so as to obtain a light yellowcrystalline product, referred to as complex E7 (63.5% yield; 107 mg).The reaction scheme for producing the complex E7 is represented asfollows:

The spectrum analysis for the complex E7 is: ¹H NMR (400 MHz, CDCl₃, 298K) δ 9.38 (s, 1H), 7.80-7.85 (m, 4H), 7.62 (s, 1H), 7.50-7.55 (m, 3H),7.44-7.48 (m, 4H), 7.17-7.21 (m, 2H), 6.95 (s, 1H), 6.66 (dd, J=2.1, 6.1Hz, 1H), 3.77 (d, J=11.5 Hz, 2H), 1.27 (s, 9H), ¹⁹F NMR (400 MHz, CDCl₃,298 K) δ −61.17 (s, 3F), −62.17 (s, 3F).

Comparative Example CE

The four-coordinated platinum (II) complex CE of Comparative Example wasmade according to the Example 1 disclosed in U.S. Pat. No. 6,963,005B2.The reaction scheme for producing the complex CE is represented asfollows:

[The Emission Peak Maximum and Quantum Yield]

Each of the complexes E1 to E7 and CE obtained from Examples 1 to 7 andComparative Example was subjected to a detection process to detect avisible emission spectrum and its emission peak maximum at roomtemperature (298 K) using a fluorescence spectrometer (purchased fromEdinburgh Instruments; Model no.: FL928P), and the resultant data areshown in FIG. 1 and Table 1. The quantum yield at solid state wasmeasured using an integrating sphere (purchased from EdinburghInstruments), and the resultant data are shown in Table 1.

TABLE 1 Complex E1 E2 E3 E4 E5 E6 E7 CE Excitation 420 390 350 380 390360 370 360 Wavelength (nm) Emission 496 495 488 477 474 470 472 460peak Maximum (nm) Quantum 76.6 71.2 74.9 91.9 89.8 80.8 100 56 Yield (%)

As shown in FIG. 1 and Table 1, the complexes E1 to E7 obtained fromExamples 1 to 7 of the present invention have the emission peak maximaranging from 470 nm to 496 nm, which demonstrates that the complexes E1to E7 emit blue light to blue-green light when they are excited.Additionally, the complexes E1 to E7 have the blue light emissionquantum yield ranging from 71.2% to 100%. The blue light emissionquantum yield of the complex CE is 56%. Therefore, the blue lightemission quantum yield of the complexes E1 to E7 is about 27-78% higherthan that of the complex CE.

To sum up, when the phosphorescent four-coordinated platinum (II)complexes according to this invention are excited, the complexes couldemit blue light to blue-green light and have superior blue lightemission quantum yield ranging from 71.2% to 100%. The abovementionedcomplexes are suitable for use in blue light and white lightphosphorescent OLED.

While the present invention has been described in connection with whatare considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements within thespirit and scope of the broadest interpretation so as to encompass allsuch modifications and equivalent arrangements.

What is claimed is:
 1. A phosphorescent four-coordinated platinum (II)complex represented by formula (C):

where Y represents N or P; R¹, R², R³, R⁴, R⁵, R⁶, R⁹, R¹⁰, R¹¹, and R¹²are the same or different, and independently represent hydrogen, or asubstituted or unsubstituted organic group; and

represents

or

when

represents

X represents C—R⁸ or nitrogen; R⁷ represents a substituted orunsubstituted organic group; and R⁸ represents hydrogen or a substitutedor unsubstituted organic group; and when

represents

ring A represents a substituted or unsubstituted bridged carbocyclicring.
 2. The phosphorescent four-coordinated platinum (II) complexaccording to claim 1, wherein: Y represents N; R¹ and R² independentlyrepresent a substituted or unsubstituted phenyl group; R³, R⁴, R⁵, andR⁶ independently represent hydrogen, a C₁-C₁₃ alkyl group, or asubstituted or unsubstituted aryl group with the proviso that at leastone of R³, R⁴, R⁵, and R⁶ is not hydrogen; R⁹, R¹⁰, R¹¹, and R¹²independently represent hydrogen, a C₁-C₄ alkyl group, or a C₁-C₄haloalkyl group; R⁷ represents a C₄-C₁₂ alkyl group, a C₁-C₄ haloalkylgroup, or a substituted or unsubstituted aryl group; R⁸ representshydrogen, a C₁-C₁₂ alkyl group, a C₁-C₄ haloalkyl group, or asubstituted or unsubstituted aryl group; and said ring A represents asubstituted or unsubstituted C₆-C₁₀ bridged carbocyclic ring.
 3. Thephosphorescent four-coordinated platinum (II) complex according to claim2, wherein R⁵ represents a tert-butyl group or a 2,6-diisopropyl phenylgroup.
 4. The phosphorescent four-coordinated platinum (II) complexaccording to claim 2, wherein R⁷ represents a tert-butyl group, atrifluoromethyl group, or a 2-trifluoromethyl phenyl group.
 5. Thephosphorescent four-coordinated platinum (II) complex according to claim2, wherein R¹⁰ represents hydrogen or a trifluoromethyl group.
 6. Thephosphorescent four-coordinated platinum (II) complex according to claim2, wherein R³, R⁴, and R⁶ represent hydrogen.
 7. The phosphorescentfour-coordinated platinum (II) complex according to claim 1, which hasan emission peak maximum ranging from 470 nm to 530 nm.
 8. Thephosphorescent four-coordinated platinum (II) complex according to claim7, wherein said emission peak maxima ranges from 470 nm to 500 nm.